Python Fire serializes the return value of a wrapped function but does not
use that value as the process exit code. Error paths in main() that used
or therefore caused the process to exit 0, swallowing
fatal errors and argument-validation failures.
Raise SystemExit(1) on every error path so batch_runner returns a non-zero
exit code when it cannot run. Success paths (e.g. --list_distributions) are
left unchanged.
ClosesNousResearch/hermes-agent#86524.
